Welcome to the NavList Message Boards.


A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding

Compose Your Message

Add Images & Files
    Re: JPL ephemeresis and Nautical Almanac - speed of light question
    From: John D. Howard
    Date: 2018 Apr 3, 15:15 -0700

    Brad and Frank,

    Yes, I agree with all you both said but if you re-read Rafal's first post he said he wanted to generate a Nautical Almanac for a day.  Yes the JPL data is for solar system bodies - it was established for the US military and NASA and rocket ships and the like ( like the GPS system ).

    My main point was for CelNav we use the apparent position of the sun, stars, and planets ( OK, the Moon too ).  Longitude is based on local apperent solar time.  No need to apply 20 arc seconds per year to a sextant reading that is timed to one second of time (  .25 arc minutes ).  The JPL data is great but not the best source of information when writing a Almanac program.  There are many, simple formula to get the sun's Dec and the EOT and to compute sideral time to the requirements of CelNav.

    My question was more to find out if Rafal's goal was to generate a Nav Almanac or to use JPL data to generate an almanac.  IMHO the JPL route would be a lot of work and over-kill but I agree with you that it can be done.

    John H.

    Browse Files

    Drop Files


    What is NavList?

    Join NavList

    (please, no nicknames or handles)
    Do you want to receive all group messages by email?
    Yes No

    You can also join by posting. Your first on-topic post automatically makes you a member.

    Posting Code

    Enter the email address associated with your NavList messages. Your posting code will be emailed to you immediately.

    Email Settings

    Posting Code:

    Custom Index

    Start date: (yyyymm dd)
    End date: (yyyymm dd)

    Visit this site
    Visit this site
    Visit this site
    Visit this site
    Visit this site
    Visit this site